Logs: Fix total bytes process calculation (#24691)

- log stats for Loki are per query
- this change tracks the query stats by refId, preventing the summing of
    the same stats across multiple series of the same response.

public/app/core/logs_model.ts

@@ -384,14 +384,20 @@ export function logSeriesToLogsModel(logSeries: DataFrame[]): LogsModel | undefi
 
   // Hack to print loki stats in Explore. Should be using proper stats display via drawer in Explore (rework in 7.1)
   let totalBytes = 0;
+  const queriesVisited: { [refId: string]: boolean } = {};
   for (const series of logSeries) {
     const totalBytesKey = series.meta?.custom?.lokiQueryStatKey;
+    // Stats are per query, keeping track by refId
+    const { refId } = series;
+    if (refId && !queriesVisited[refId]) {
       if (totalBytesKey && series.meta.stats) {
         const byteStat = series.meta.stats.find(stat => stat.displayName === totalBytesKey);
         if (byteStat) {
           totalBytes += byteStat.value;
         }
       }
+      queriesVisited[refId] = true;
+    }
   }
   if (totalBytes > 0) {
     const { text, suffix } = decimalSIPrefix('B')(totalBytes);